1. Field of the Invention
The present invention relates to a projector screen used as an image-displaying medium, and more particularly to a projector screen having an improved horizontal view angle.
2. Description of the Related Art
The direct-view type screen of a conventional image-displaying means, for example, a television, uses a cathode-ray tube (CRT). For larger screens, however, the use of a cathode-ray tube is not practical because it is difficult to make a large CRT. Even if technical problems associated with making large CRTs could be overcome, the weight of a CRT also increases accordingly, so that it is difficult to transport and assemble a large CRT into a finished device. Therefore, an image projection system such as a projection television or video projector has been developed.
FIGS. 1 and 2 show two examples of a conventional image projection system. Such a system generates an image by using a specially manufactured small CRT 1 or image-displaying means 2 such as a liquid crystal display element or a polymer dispersed liquid crystal. Then, the generated image is amplified by using an optical lens, e.g., projection lens 3, for projection onto a large screen.
Conventionally, there are two types of image projection systems, i.e., a frontal-projection type projector (front type) and a rear-projection type projector (rear type). Typical rear-projection type projectors, such as those shown in FIGS. 1 and 2, have advantages in that they can be manufactured with a slimmer body than the frontal-projection type projector, and can provide a displayed image of better brightness.
The rear type projector is used for various kinds of apparatus such as a flight simulator, a traffic signal light, a video monitor, a microfilm reader, and a general rear-projection type display using a film medium for generating an image which can be observed by a user. These apparatus include a projector which generates an image on a screen by projecting light, from an image source situated behind the screen, along a projection axis to the front of the screen. A viewer is situated in front of the screen, and when there are many such viewers, the horizontal viewing angle must be large to allow all of the viewers to see a bright image. Also, it is desirable to have a large horizontal viewing angle so that a viewer can be situated at positions other than directly in front of the screen.
FIG. 3 is a schematic perspective view showing the cross-sectional structure of a screen for a conventional projector. To display an image of nearly uniform luminance over a wide viewing angle by deflecting the rays emitted from an image source, the screen is equipped with Fresnel lens 11 for generating parallel light by receiving the light magnified by a projection lens. In front of Fresnel lens 11, there are plural lenticular lenses 12 extending in parallel with one another (hereafter collectively called a lenticular lens system). The lenticular lens system serves as a light-spreading means for forming an image by spreading the parallel light passed through Fresnel lens 11. In front of the lenticular lens system, namely, at the viewer's side, is screen protection panel 13 of an acrylic material. Also, between the rear side of screen protection panel 13 and the front side of the lenticular lens system, projecting part 12a of a predetermined height is formed for absorbing part of light spread from a convex surface of the individual lenticular lenses 12. Projecting part 12a is formed by black stripes 12b painted with an opaque ink or the like formed between adjacent lenticular lenses 12 forming the lens system on the tip of projecting part 12a. This allows the contrast of the image formed in front of lenticular lens 12 to be improved.
However, in a conventional screen for a projector, projecting part 12a having black stripe 12b extends outward from the surface of the lenticular lens system so that a light-scattering angle of the individual lenticular lenses 12 of the lenticular lens system is limited. See FIG. 4. This limited light-scattering angle restricts the horizontal angle for viewing an image on the screen.